Methyl arsine oxide method of controlling soil-borne pythium fungi



United States Patent 3,338,780 METHYL ARSINE OXIDE METHOD OF CONTROL-LING SOIL-HORNE PYTHIUM FUNGI Arthur Schwerdle, Vinelaud, N.J., assignorto Vineland Chemical Company, Vineland, N.J., a partnership No Drawing.Filed Aug. 10, 1964, Ser. No. 388,679 10 Claims. (Cl. 167-22) Thepresent invention relates to a novel method for the control andtreatment of soil-borne fungus diseases of plants; and moreparticularly, the present invention relates to the control of soil-bornefungi, especially snow mold. Pythium, Helminthosporium-Curvularia andRhizoctonia fungi, in the soil in their various life stages, includingthe sclerotia stage.

Pythium, Helminthosporium-Curvularia and Rhizoctonia are probably themost important fungi which attack the roots of plants in general.Rhizoctonia causes seedling damping-off in a large number of crops,including vegetables, ornamentals, field crops and citrus; for example,it has been estimated that Louisiana cotton growers lose about 5% oftheir crop because of soreshin of cotton seedlings due to thissoil-borne fungus. Pythium also causes damping-off of plant seedlings,like tomatoes. Members of the Helminthosporium-Curvularia complex havecaused severe root rot on seedlings of rice and wheat, and blight inoats.

There are two common types of snow mold diseases on turf grasses. Graysnow mold (snow scald or winter scorch) caused Typhula, is thepredominant type of snow mold found in New England. Pink snow mold orFusarium patch, caused by Calongc tria nivalis (Fusarium rii'vale), iscommon in Washington State along with the gray snow mold. Pythium orgrease spot (caused by Pythium aphanidermatwm) is a disease of turfgrasses common to the southern part of the United States.Helminthosporium-Curvularia complex also causes a serious disease ofturf grasses. Brown patch, caused by Rhizoctonia solani causesconsiderable damage to turf grasses, and it, like Pythium, has beenknown to destroy entire putting greens overnight.

The foregoing fungi are soil borne and hence exist in the soil invarious stages of the life cycle: spore, 'sclerotia and mycelium. In thesclerotia stage, these pathogens are resting bodies which have proven tobe highly resistnat to chemicals, making control diflicult.

of the soil to serve as a repository or life-supporting medium ofpotential infection of plants is greatly reduced or extinguished.

It is another object of the present invention to provide a method forthe control of snow mold, Pythium, Helminthosporium-Curvularia andRhizoctonia fungi in soil.

These and other objects will become apparent from a consideration of thefollowing specification and the claims.

The method of the present invention comprises applying, to soilcontaining fungi injurious to plants, an aqueous solution of methylarsine oxide at a rate of between about; 0.2 and about 8 pounds ofmethyl arsine oxide per acre.

It has been found? that methyl arsine oxide is highly effective in thesoil against soil-borne fungi injurious to desirable plants, at rates ofapplications which can be well below the level 'at which the methylarsine oxide is phytotoxic toward desirable plants, including turfgrasses, which maybe growing in the soil. It has been found that methylarsine oxide does not become inactiyated by materials in the soil atleast until it has exerted its effect on the fungi organism. Moreover,it has been found that methyl arsine oxide, upon penetrating the soil,attacks and kills the fungi therein in the normally resistant sclerotia,or resting, stage, as well as in the spore and mycelium stages. Thus,unexpectedly, methyl arsine oxide is able, in effect, to greatly reduceor extinguish the ability of the treated soil to harbor the harmfunfungi and to serve as a repository from which the fungi may attackplants, including roots, tubers, stems and foliage. Unlike the prior artwhich treated the disease itself at the side of infection, the presentinvention treats the pathogen source of the disease or infection, awayfrom the side of the infection, thereby more effectively preventingsubsequent infection.

The rates of application presently found to be suitable range from about0.2 to about 8 pounds of methyl arsine oxide per acre. If there arepresent in the soil, desirable plants, like surf grass, which would becontacted by the solution by the particular mode of appli- Priorfungicides are largely limited in their ability to pass through soil andattack all three stages of the life cycle, including sclerotia, of theabove-mentioned pathogens. Moreover, a successful fungicide againstthese pathogens must be effective at rates which are non-injurious tothe desirable plant roots that may be present in the treated soil, andmany fungicides do not have this ability.

Methyl arsine oxide has been suggested as having some fungicidal utility(see, for example, US. Patents 1,565,237, 1,652,291 and 2,054,062).However, such utility has been confined to treatment-of the fungusdisease itself at the site of the infection, such as on the seed orplant.

It is the principal object of the present invention to provide a novelmethod for controlling soil-borne fungi.

It is a further object of the present invention to provide a method forcontrolling soil-borne fungus diseases, injurious to plants, by treatingsoil to interrupt the life cycle of the harmful fungi therein wherebythe ability cation, like broadcast spraying, it is recommended thateither a rate in the lower portion of the range be used or theapplication, if in the upper portion of the rate range, be followed byliberal application of water to wash methyl arsine oxide from the plantsinto the soil. In most cases, a rate below about 1.5 pounds per acrewill be suflicient whether or not there are desirable plants presentwhich are contacted by the solution.

As stated, the methyl arsine oxide will be applied as an aqueoussolution thereof, usually by spraying. The water in the solution isprimarily a vehicle to aid in theeasy'dispersal of-thecompound over thearea and to the soil at the desired rate. Once the methyl arsine oxideis applied to the soil, distribution of the compound into the s-oil.willdepend upon water content of the soil at the time of application, watersubsequently applied to .the treated soil (rain or after-watering) andnatural diffusion of the compound, by virtue of the nature of the soil,in vapor-or liquid phase. Hence, as far as the application of thecompound to the soil is concerned, the concentration of the methylarsine oxide in the solution applied may range from about 25 p.p.m. toabout 100,000 p.p.m.

The principal object to be achieved is to provide a concentration ofmethyl arsine oxide in the soil water 8) which is effective against thefungi. The minimum such concentration is about 1 p.p.m. (1 part'ofmethyl arsine oxide per million parts of water in the soil). As apractical matter the upper limit need be no more than about 125 p.p.m.As an illustration, taking a soil that contains by weight, of water andapplying the methyl arsine oxide at a rate of 1 pound per acre, resultsin a concentration of methyl arsine oxide in the soil water of about 8p.p.m., assuming the methyl arsine oxide penetrates to about 6 inchesinto the soil. Because of the amount of soil water involved, the amountof Water added with the methyl arsine oxide is negligible. It will berealized that the concentration of methyl arsine oxide will not beuniform throughout the entire area or throughout the entire depth ofpenetration, and that the concentration is probably higher nearer thesurface where, in any event, most of the organisms will be found. Theconcentration figures given above, therefore, are average, and may beconsidered as representing the average concentration in the first 6inches of soil whether or not the methyl arsine oxide has actuallypenetrated to that depth.

While the methyl arsine oxide may be the only active ingredient presentin the solution, applied, it will be obvious that various adjuvants,like wetting agents, stabilizers, plant nutrients, other pesticides,including fungicides, and the like, may be included if desired.

As stated, the present invention is particularly adapted for the controlof soil-borne fungi injurious to desirable plants. One area where thepresent invention finds wide application is in the treatment of soilbearing turf grass. Such turf grasses include bent grasses, like AstoriaColo-. nial, seaside creeping and velvet bpntgrasses; fescues, likeChewings fescue; bluegrass, like Merion and Kentucky bluegrasses; ryegrasses, and the like.

As illustrative of the effects of methyl arsine oxide on snow mold inturf grasses, methyl arsine oxide is compared with several priorfungicides. Each of the materials, set forth in the table below, wasrandomly replicated three times on square foot plots of seaside creepingbentgrass maintained as putting greens. Only one application was made.Each treatment was applied with a power sprayer equipped with anagitator, in the fall of the year at a rate of 10 gallons of solutionper 1,000 square feet of turf. Disease ratings were taken the followingMarch in terms of the percentage of each plot injured by Typhula snowmold (gray snow mold). The ratings of the three replicates were averagedand are set forth in the following table:

The concentration of methyl arsine oxide in the applied solution wasabout 200 p.p.m.

As illustrative of the effects of methyl arsine oxide against Pythium inthe presence of soil, the following tests have been carried out:

One inch of soil is placed on top of a one inch styrene foam plug in aglass shell vial having a small hole in the bottom to allow entrappedair to escape. On this layer of soil is placed a 5 mm. disc of agar andmycelium of Pythium aphanidermatum. An additional one inch of sterilesoil is placed on top of this disc. 8 ml. of various aqueous solutionsof varying concentrations of methyl arsine oxide are then carefullypoured on top of the top layer of soil and allowed to drain through thesoil. Each concentration of solution is replicated three times inseparate vials. After tWenty-four hours incubation at 26 C., the agarfungus-containing discs are removed and planted on the corn meal-agarplates which are then incubated at 26 C. Results are recorded as thenumber of discs showing growth or lack of growth The results aretabulated as follows:

1 This means no growth in three replicates. 2 This means growth in allthree replicates.

Tests similar to the foregoing were also run using Pythium ultimum withthe following results:

TABLE III Growth after Days Incubation Treatment Cone.

ControL 3+ 3+ 3+ 3+ 3+ Methyl arsine oxide i. 50 3 3- 3 3 3- Similartests, but using mycelium of Rhizoctom'a solani, gave the followingresults:

TABLE IV Growth after Days Incubation Treatment Conc.

(p-D-nL) Control 2+ 2+ 3+ 3+ 3+ Methyl arsine oxide 10 3- 3- 3 3- 3- 53- 3- 3- 3 3- Similar tests, but using sclerotia of Rhizoctonia so lani,gave the following results:

TABLE V Growth alter Days Cone. Incubation Treatment (p.p.m.)

Control 3+ 3+ 3+ Methyl arsine oxide 3- 3- 3- 3- 3- 3- 3- 3 3- 3- 3 3 33- 3- In tests of a similar nature in which Curvularia spores were usedand the test specimens were incubated at 20 C. for 20 hours, control wasachieved at 40 p.p.m. concentration of methyl arsine oxide and 98-99%control was obtained at 20 p.p.m. Field tests on seaside creeping andvelvet bentgrasses during the summer, with applications at the rate of0.37 pounds of methyl arsine oxide per acre and a concentration of about100- p.p.m. in water at intervals of 8, l0, 8, 8, 9, 1O, 10, 8, l2 and10 days, provided good control of the Helminthosporium-Curvulariacomplex.

Field tests were conducted during the summer on a practice putting greenof creeping bentgrass that is usually severely attacked by brown patch(Rhizoctonia solani). Two treatments with methyl arsine oxide, one at acon centration of methyl arsine oxide in water at about 33 p.p.m., theother at a concentration of 100' p.p.m., and both at a rate of .35 poundof methyl arsine oxide per acre, and an untreated control, were randomlyreplicated three times on plots of 100 sq. ft. each. Seven applicationsat two-week intervals were made. The treatment provided excellentcontrol in that no brown patch injury was observed in any of the treatedplots, whereas the three control plots reached an average of injury dueto brown patch.

Field tests were conducted to determine control of cotton seedlingdamping-off caused by Rhizoctonia solani. Cotton seed beds were sprayed(furrow sprayed) with a solution of methyl arsine oxide (5,000 p.p.rn.)at the rate of 0.2 pound of methyl arsine oxide per acre. This gave a10% greater emergence of cotton seedlings than the untreated controlplots.

Tests in the field. have also shown the effectiveness of methyl arsineoxide against Pythium. In Smyrna, Ga., during the late summer whenPythium disease is prevalent, plots of clay soil were laid outpermitting two replicates for each treatment and a control. Each plotwas watered well with water containing a nonionic wetting agent (alkylaryl polyether alcohol) in an amount of ml. of wetting agent per 10gallons of water per 1000 square feet. Then aqueous solutions of methylarsine oxide, all at a concentration of 100 ppm. (and all containingsaid wetting agent on the basis of 1 ml. thereof per 2.5 gal. water),were applied to selected plots (two replicates) at rates of 3.65, 5.47and 7.3 pounds per acre, respectively. The next day, a selected portionof each plot was seeded with annual rye grass, at the rate of 60 poundsof seed per 1000 sq. ft., mulched and watered. On each of threesuccessive days thereafter, selected portions of each plot weresimilarly seeded, mulched and watered. Each day after planting, themulch on each test area was moistened to provide conditions conducive toPythium. On the tenth day from the initial seeding, the mulch was rakedfrom the areas seeded the first three days, and all plots werefertilized with an aqueous solution of a commercial watersoluble23-21-17 turf fertilizer. The seed in all plots, including the control,germinated and grew, and there was no significant difference in theappearance of the grass on each plot. However, on the eleventh day afterthe initial seeding, the grass on the control plot had thecharacteristic gray appearance of Pythium, and within a few days moreall the grass in the control plot was dead. The grass on all the treatedplots remained healthy.

Modification is possible in the techniques of application and inorganisms treated without departing from the scope of the invention.

I claim:

1. The method of controlling soil-borne Pythium fungus diseasesinjurious to plants which comprises applying to soil containing Pythiumfungi injurious to plants an aqueous solution of methyl arsine oxide inan amount substantially to kill said fungi.

2. The method of claim 1 wherein the methyl arsine oxide is applied at arate of between about 0.2 and about 8 pounds per acre.

3. The method of claim 2 wherein the methyl arsine oxide is applied at arate not over about 1.5 pounds per acre.

4. The method of claim 1 wherein the methyl arsine oxide is applied at arate to provide, in the first six inches of soil, a concentration ofmethyl arsine oxide in the soil water of between 1 and about parts permillion.

5. The method of claim 2 wherein the soil contains no desirable plantsgrowing therein.

6. The method of claim 2 wherein the soil contains desirable plantsgrowing therein; wherein the methyl arsine oxide solution is sprayedover the area including the plants at a rate above about 1.5 pounds peracre, and wherein water is subsequently applied to wash methyl arsineoxide from the plants to the soil.

7. The method of claim 6 wherein the soil contains growing turf grass.

8. The method of claim 3 wherein the soil contains growing turf grass.

9. The method of claim 1 wherein said Pythium fungi is found togetherwith at least one of those selected from the group consisting of snowmold, Helminthosporium- Curvularia and Rhizoctonia.

10. The method of claim 1 wherein at least a portion of said fungi is inits sclerotia stage of the life cycle.

References Cited UNITED STATES PATENTS 1,565,237 12/1925 Schmidt et al167-15 1,652,291 12/1927 Tanner 167-41 2,678,265 5/1954 Schwerdle 712.73,056,668 10/1962 Sprague 712.1

FOREIGN PATENTS 1,079,886 4/ 1960 Germany.

OTHER REFERENCES Adams et al.: Progress Report on Methyl Arsine Oxide, 2pp., reprint Golf Course Reporter, May 1964.

LEWIS GOTTS, Primary Examiner. S. K. ROSE, Assistant Examiner,

1. THE METHOD OF CONTROLLING SOIL-BORNE PYTHIUM FUNGUS DISEASESINJURIOUS TO PLANTS WHICH COMPRISES APPLYING TO SOIL CONTAINING PYTHIUMFUNGI INJURIOUS TO PLANTS AN AQUEOUS SOLUTION OF METHYL ARSINE OXIDE INAN AMOUNT SUBSTANTIALLY TO KILL SAID FUNGI.